Traditionally, methods for sulfonation of hydrocarbon compounds have included the use of fuming sulfuric acid and liquid or gaseous SO.sub.3. Sulfonation is usually carried out in either film or free annular jet reactors.
Sulfonation methods using these types of reactors have been problematic for several reasons. First, the high viscosity of the sulfonation reaction product interferes with the sulfonation of remaining unreacted feedstock, and results in lowered yields of final sulfonated reaction product. Secondly, the high viscosity of the sulfonated reaction product requires the use of scrapers and/or solvents to keep the sulfonated product moving through the reactor. An example of a method for sulfonation using a thin film reactor is set forth in U.S. Pat. No. 3,620,684 to Brooks. This patent discloses an improved method for the sulfonation of organic reactant by means of a reaction between a liquid organic reagent and sulfur trioxide vapor in a thin film reactor. An example of a method of sulfonation using a jet reactor is set forth in U.S. Pat. No. 4,111,438 to Brooks.
Other prior art methods have included the use of SO.sub.3 or H.sub.2 SO.sub.4 for sulfonation. These methods also present problems. One such problem arising from the use of SO.sub.2 is that SO.sub.2 is a gas at room temperature and consequently requires a pressurized or cold reactor. This adds to the cost of manufacturing. The use of H.sub.2 SO.sub.4 results in contaminated end product, thus requiring additional steps for recovering the product For example, the use of H.sub.2 SO.sub.4 results in large quantities of inorganic salts present in both the end product and the waste water. The inorganic salts are undesirable because when the sulfonated product is used in emulsified products such as hand creams, liquid detergents, liquid soap and shampoos, the inorganic salts cause phase separation and result in unusable products.
Various other references teach the sulfonation of organic feedstocks in recycle loop reactors. Examples of these are set forth in U.S. Pat. No. 4,226,796 to Akred and U.S. Pat. No. 4,261,916 to Crosby. The Akred patent teaches the use of sulfur trioxide as a sulfonating agent in a recycle loop reactor where the feedstock is diluted with its recycled sulfonation product. To moderate the effects of the heat of reaction, Akred teaches that in some instances it is necessary to use a solvent, such as carbon tetrachloride, when the reaction product has a high melting point or is highly viscous. Also, in this type of reaction there is significant heat evolved due to the reaction necessitating the use of heat exchangers to remove excess heat.
The Crosby patent discloses a design for a turbulent flow plate mixer for mixing at least two fluids in the recycle loop reactor. This patent discusses that significant heat of reaction is produced during sulfonation with sulfur trioxide. To moderate the effects of the heat of reaction, Crosby states that it may be necessary to dilute the sulfur trioxide With a diluent such as a chlorinated hydrocarbon, which may be undesirable. The prior art methods disclosed in Akred and Crosby are undesirable because they utilize solvents that are difficult to dispose of, such as chlorinated aliphatic hydrocarbons (e.g. carbon tetrachloride and MeCl.sub.2) and fluorocarbons. The solvents result in contaminated end products, and are toxic, carcinogenic and adversely effect the environment.
Unlike the prior art methods mentioned above, the process of the present invention utilizes recycled SO.sub.3 gas obtained from a sulfonator recycler to sulfonate compounds which have been saturated into a porous inorganic material absorber. The recycling of SO.sub.3 gas for this purpose is described in U.S. Pat. Nos. 4,902,493 and 4,915,912, which are hereby incorporated by reference.
Porous inorganic material absorbers have been used in the past in some other reactions. Clay is such an absorber and has been used to heat and vaporize reactants and as a filter. However, the patents disclosed herein do not use clay as a reaction media. U.S. Pat. No. 2,448,184 to Lemmon teaches the use of fluidized clay to remove sulfuric acid after sulfonating a hydrocarbon in a sulfonation reactor with sulfuric acid. The sulfonated hydrocarbon is removed from the reactor and then contacted with adsorption clay to remove the sulfuric acid.
U.S. Pat. No. 2,654,658 to Marshall teaches the nitration of organic compounds by contacting a dense bed of heated, finely divided, suspended solids with nitric acid. The heated solids cause the nitric acid to vaporize and contact the vapors of organic compounds to be nitrated.
Upon reading these patents, it can be seen that the Lemmon and Marshall references do not teach the use of a fluidized clay as a media on which reaction actually occurs. Lemmon uses the clay only as a filter. Marshall uses a fine solid media only for heating and vaporizing a reactant.
Therefore, it is the primary object of the present invention to provide a method for sulfonating a compound which employs a reusable porous inorganic material absorber as a media on which the sulfonation reaction occurs.
It is a further object of the invention to provide a method for sulfonation which results in a sulfonated product containing less than 10 percent by weight inorganic salts, based on total sulfonated product weight. It is yet a further object of the present invention to provide a sulfonation method which reduces the maximum process temperature of the reaction. It is yet still a further object of the present invention to use SO.sub.3 gas obtained from a sulfonator-recycler in the present sulfonation process. It is still a further object of the present invention to provide a sulfonated product containing less than 1.0 percent by weight inorganic salts based on total sulfonated product weight, by the disclosed method.